Lead producers and experts of that field agree that to satisfy environmental protection requirements of applicable laws and regulations imposed by governmental authorities, Pb recovery from exhausted batteries must be achieved by a hydrometallurgical and electrolytic method. Notwithstanding this, industrial plants for electroextracting lead from solution have not yet been constructed. The reasons for this are various, but in particular are related to the operations required for modifying the paste to make it soluble in electrolytes.
In the numerous processes currently used for the thermal recovery of lead, the various desulphurizing agents (in particular Na.sub.2 CO.sub.3, NaOH, (NH.sub.4).sub.2 SO.sub.4) are effective in eliminating SO.sub.2 from the reduction furnace off-gases, but this in itself does not solve the problems of environmental compatibility.
The disposability of by-products and the actual economy of the process are also factors. Finally, desulphurizing the paste does not completely solve the problem of applying electrochemical extraction, because not all the lead is converted into a soluble form and the lead extraction yield is incomplete. In the process of Manequini, U.S. Pat. No. 5,630,931 the past is reacted with a sodium sulphide solution. By converting all the components into PbS, the problem of completely dissolving the lead in the electrolyte is totally solved. However, this process still presents the problem of regenerating sodium sulphide from the sodium sulphate which forms in the process.
In this respect, this regeneration is effected by reduction with carbon in a furnace at 800.degree.-900.degree. C., requiring a complex plant for neutralizing the gaseous emissions generated. The financial investment is high, and can put the convenience of the entire process in doubt especially for small and medium producers.